The present invention generally relates to fabricating optical integrated circuits. In particular, the present invention relates to efficiently isolating optical integrated circuits with high yields from substrates.
Water jets and abrasive water jets are commonly employed in cutting and machining operations, particularly with metal sheet and plates to effect rapid and economical cutting and related forming operations. Typical applications include cutting materials which are difficult to machine, such as stainless steels, titanium, nickel alloys, reinforced polymer composites, and the like. Such techniques are particularly advantageous to produce cutting action through very highly localized action and without delamination of composite materials.
To effect water jet cutting, a specialized nozzle assembly is employed to direct a high pressure stream through an orifice to form a water jet. Typical nozzle assemblies are formed of abrasion resistant materials, such as tungsten carbide. The orifice itself may be formed of diamond or sapphire. Abrasive particles may be added to the high speed stream of water exiting the nozzle orifice by injection into the water stream near or in the nozzle. Although a turbulent flow is typically created where the particles contact the stream, the relatively stationary or slow moving abrasive particles are accelerated and become entrained in the high speed water stream. The entrainment process tends to disperse and decelerate the water stream while the abrasive particles collide with the nozzle wall and with each other. However, relatively wide kerfs undesirably result from the dispersed jet streams. Furthermore, energy is wasted when a dispersed stream is employed, and the nozzle is rapidly worn, even when made from abrasion resistant materials, such as tungsten carbide and the like.
While it may be desirable in some instances to employ abrasives in water jets, injecting abrasive particles into a water stream often results in clogging of the cutting head and/or nozzle. And the smaller the abrasive particles, the more likely clogging occurs.
Planar lightwave circuits (PLCs) are optical circuits laid out on a silicon wafer. PLCs, which typically contain one or more planar waveguides often used in arrayed waveguide gratings, are used as components in constructing an optical communication system. Optical communication systems permit the transmission of large quantities of information. With ever increasing internet traffic, greater demands are placed on optical communication systems, and their corresponding components.
A plurality of optical integrated circuits (OICs) including PLCs are typically fabricated on a single substrate or wafer. For example, a substrate may be fabricated with 30 to 40 OICs thereon. Individual OICs are isolated using a specialized saw to dice the substrate. However, OICs have a regular (consistent), non-rectangular geometry. Straight-line dicing using a saw consequently leads to the inefficient isolation of individual OICs from a substrate. Referring to FIG. 1, a substrate 100 with a plurality of PLCs 102 thereon is shown. Referring to FIG. 2, when individual PLCs 102 are isolated from the substrate 100 using a saw (square dicing), several PLCs 104 are destroyed while only one PLC 106 is recovered. Often times, two to four PLCs are destroyed for each PLC that is recovered.
Moreover, unlike machining metal substrates, PLC substrates and the components thereon are often made of monocrystalline silicon, silicon dioxide, various oxides and silicates, and other materials that have a very brittle nature. The brittle nature of such materials results in cracks and chips in the substrate or the components thereon. Since a plurality of OICs are fabricated in close proximity to one another, even small chips and cracks can render the OICs fatally defective. Cutting the brittle materials thus requires a high degree of care so as not to destroy the substrate. For this reason, specialized saws are employed to cut PLC substrates.
There is an unmet need in the to art to improve the current yields of OICs/PLCs from substrates.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Rather, the sole purpose of this summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented hereinafter.
The present invention provides methods and systems for curvilinear cutting of brittle materials that permits the isolation of OICs from a substrate with high yield. The present invention provides methods and systems for curvilinear cutting of brittle materials while mitigating or eliminating edge chipping, cracking, and other degrading effects. Wet injecting a water soluble polymer into a water jet cutter improves the cut quality of brittle materials by increasing the coherency of the cutting stream and thus permit increased standoff distances. Increased standoff distances permit in situ inspection and monitoring of the curvilinear cutting process. Monitoring is particularly useful when cutting extremely brittle materials since chips and cracks are likely to occur. Wet injecting a water soluble polymer into a water jet cutter also minimizes clogging of the cutting head by abrasives that may or may not be present. As a result, the present invention maximizes the yield of non-rectangular OICs from a single substrate. The present invention also correspondingly promotes maximizing the number of non-rectangular OICs that may be fabricated on a single substrate since isolation thereof in high yield is enabled.
One aspect of the invention relates to a method of cutting a brittle substrate comprising a non-rectangular shaped optical integrated circuit, involving providing the brittle substrate comprising a plurality of non-rectangular shaped optical integrated circuits on a water jet cutting system, the brittle substrate positioned proximate a cutting head of the water jet cutting system; supplying a high pressure water stream to the cutting head; wet injecting a mixture of water and at least one water soluble polymer into the water stream; and water jet cutting the brittle substrate in a curvilinear manner to separate at least one of the plurality of non-rectangular shaped optical integrated circuits without fatally damaging an adjacent optical integrated circuit.
Another aspect of the invention relates to a system for separating a plurality of non-rectangular shaped optical integrated circuits formed on a brittle substrate, containing a brittle substrate holder for holding the brittle substrate comprising the plurality of optical integrated circuits; a supply of a mixture of water and at least one water soluble polymer connected to a water jet cutting device; a water supply connected to the water jet cutting device; the water jet cutting device comprising a cutting head; and the cutting head comprising a nozzle for expelling a jet stream under pressure for cutting the brittle substrate in a curvilinear manner, at least one of the brittle substrate holder and the cutting head movable in a curvilinear manner.
Yet another aspect of the invention relates to a method of water jet cutting a silicon substrate in a curvilinear manner, involving providing the silicon substrate on a water jet cutting system, the silicon substrate positioned proximate a cutting head having an orifice of the water jet cutting system; wet injecting a mixture of water and at least one water soluble polymer into a water stream; supplying the water stream comprising at least one water soluble polymer to the cutting head under high pressure; expelling a polymer water jet from the orifice to contact the silicon substrate; and moving the silicon substrate in a curvilinear manner in relation to the cutting head to cut the silicon substrate in a curvilinear manner while reducing at least one of chipping the silicon substrate and cracking the silicon substrate.